1020 



PHYSIOLOGY 



THE ACTION OF ADRENALINE ON THE HEART 



The medullary part of the suprarenal glands forms and secretes into the 

 blood stream a substance, adrenaline, which has a marked action both on the 

 heart and blood vessels and plays therefore an important part in the regula- 

 tion of the circulation. Whether this secretion is a constant one has not yet 

 been fully ascertained,' but there is no question that under certain specified 

 conditions there may be a marked influx of this substance into the blood 

 stream. The action of adrenaline on any part of the body is practically 

 identical with that of excitation of the sympathetic nerve supply to the same 

 part. Its isolated action on the heart is best studied on the perfused heart or 



FIG. 460. 



Intraventricular pressure tracings (left ventricle) from dog's heart (heart-lung 

 preparation). (To be read from right to left.) The scale shows pressure 

 in mm. Hg. 



a. Under influence of adrenaline. 



6. Under simultaneous influence of adrenaline and C0 2 (15 per cent.) (PATTERSON). 



in the heart-lung preparation. On adding ^V mgm. of this substance to the 

 500 c.c. of blood circulating through the heart-lung preparation, a maximum 

 effect is at once produced and this lasts for 15 to 20 minutes. The action is, 

 like that of the sympathetic nerve, accelerator and augmentbr. Through 

 its influence on the sinus or the sino-auricular node, the rhythm of the heart 

 is markedly increased, in the dog to about 240 per minute. At the same time 

 the energy of each contraction is augmented. This is especially shown in a 

 heart which is beginning to fail and is therefore undergoing a certain degree 

 of dilatation. Directly the adrenaline reaches the heart, the contractions 

 become extremely energetic so that the heart rapidly diminishes in volume, 

 the venous pressure falls, and the bipod flowing into it at each diastole is 

 thrown out with violence into the aorta. The more powerful beat enables 

 the output of the heart at each beat to be maintained or even increased, in 

 spite of the shorter duration of the systole. With each beat the maximum 

 pressure in the ventricle therefore rises to a marked extent (see Fig. 460). 



